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/**
* @file sysoff.c
* @brief Implements the system offset estimation method.
* @note Copyright (C) 2012 Richard Cochran <richardcochran@gmail.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <sys/ioctl.h>
#include <linux/ptp_clock.h>
#include "print.h"
#include "sysoff.h"
#define NS_PER_SEC 1000000000LL
static void print_ioctl_error(const char *name)
{
if (errno == EOPNOTSUPP)
pr_debug("ioctl %s: %s", name, strerror(errno));
else
pr_err("ioctl %s: %s", name, strerror(errno));
}
static int64_t pctns(struct ptp_clock_time *t)
{
return t->sec * NS_PER_SEC + t->nsec;
}
static int sysoff_precise(int fd, int64_t *result, uint64_t *ts)
{
struct ptp_sys_offset_precise pso;
memset(&pso, 0, sizeof(pso));
if (ioctl(fd, PTP_SYS_OFFSET_PRECISE, &pso)) {
print_ioctl_error("PTP_SYS_OFFSET_PRECISE");
return -errno;
}
*result = pctns(&pso.sys_realtime) - pctns(&pso.device);
*ts = pctns(&pso.sys_realtime);
return 0;
}
static int64_t sysoff_estimate(struct ptp_clock_time *pct, int extended,
int n_samples, uint64_t *ts, int64_t *delay)
{
int64_t t1, t2, tp;
int64_t interval, timestamp, offset;
int64_t shortest_interval, best_timestamp, best_offset;
int i = 0;
if (extended) {
t1 = pctns(&pct[3*i]);
tp = pctns(&pct[3*i+1]);
t2 = pctns(&pct[3*i+2]);
} else {
t1 = pctns(&pct[2*i]);
tp = pctns(&pct[2*i+1]);
t2 = pctns(&pct[2*i+2]);
}
shortest_interval = t2 - t1;
best_timestamp = (t2 + t1) / 2;
best_offset = best_timestamp - tp;
for (i = 1; i < n_samples; i++) {
if (extended) {
t1 = pctns(&pct[3*i]);
tp = pctns(&pct[3*i+1]);
t2 = pctns(&pct[3*i+2]);
} else {
t1 = pctns(&pct[2*i]);
tp = pctns(&pct[2*i+1]);
t2 = pctns(&pct[2*i+2]);
}
interval = t2 - t1;
timestamp = (t2 + t1) / 2;
offset = timestamp - tp;
if (interval < shortest_interval) {
shortest_interval = interval;
best_timestamp = timestamp;
best_offset = offset;
}
}
*ts = best_timestamp;
*delay = shortest_interval;
return best_offset;
}
static int sysoff_extended(int fd, int n_samples,
int64_t *result, uint64_t *ts, int64_t *delay)
{
struct ptp_sys_offset_extended pso;
memset(&pso, 0, sizeof(pso));
pso.n_samples = n_samples;
if (ioctl(fd, PTP_SYS_OFFSET_EXTENDED, &pso)) {
print_ioctl_error("PTP_SYS_OFFSET_EXTENDED");
return -errno;
}
*result = sysoff_estimate(&pso.ts[0][0], 1, n_samples, ts, delay);
return 0;
}
static int sysoff_basic(int fd, int n_samples,
int64_t *result, uint64_t *ts, int64_t *delay)
{
struct ptp_sys_offset pso;
memset(&pso, 0, sizeof(pso));
pso.n_samples = n_samples;
if (ioctl(fd, PTP_SYS_OFFSET, &pso)) {
print_ioctl_error("PTP_SYS_OFFSET");
return -errno;
}
*result = sysoff_estimate(pso.ts, 0, n_samples, ts, delay);
return 0;
}
int sysoff_measure(int fd, int method, int n_samples,
int64_t *result, uint64_t *ts, int64_t *delay)
{
switch (method) {
case SYSOFF_PRECISE:
*delay = 0;
return sysoff_precise(fd, result, ts);
case SYSOFF_EXTENDED:
return sysoff_extended(fd, n_samples, result, ts, delay);
case SYSOFF_BASIC:
return sysoff_basic(fd, n_samples, result, ts, delay);
}
return -EOPNOTSUPP;
}
int sysoff_probe(int fd, int n_samples)
{
int64_t junk, delay;
int i, j, err;
uint64_t ts;
if (n_samples > PTP_MAX_SAMPLES) {
fprintf(stderr, "warning: %d exceeds kernel max readings %d\n",
n_samples, PTP_MAX_SAMPLES);
fprintf(stderr, "falling back to clock_gettime method\n");
return SYSOFF_RUN_TIME_MISSING;
}
for (i = 0; i < SYSOFF_LAST; i++) {
for (j = 0; j < 3; j++) {
err = sysoff_measure(fd, i, n_samples, &junk, &ts,
&delay);
if (err == -EBUSY)
continue;
if (err)
break;
return i;
}
}
return SYSOFF_RUN_TIME_MISSING;
}
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